[Arachnoiditis ossificans after repeated myelographies and spinal operations--a case report and review of the literature].

A 58-year-old female was admitted because of lumbago and dysesthesia on the lateral aspect of the left leg. She had myelographies and spinal operations 4 years ago. Metrizamide myelogram on admission revealed the findings of adhesive arachnoiditis. During operation, four plaques involving the cauda equina were found, removed and histologically proved to be osseous tissue. In reviewing the previously published cases of arachnoiditis ossificans, it is divided into two forms. One is incidentally found in the arachnoid membrane at the time of an autopsy or spinal operation. The other is a progressive form causing impairment of the spinal cord and cauda equina. Compared with the former, the latter is extremely rare. At present, there appears to be a general agreement about the pathological process to ossification in the latter. The ossified plaque has its origin in meningothelial cell clumps located at the junction of the arachnoid sheet and the trabecula. The ossification occurs secondarily as a result of degenerative change in these clumps after myelography, spinal operation, subarachnoid hemorrhage, spinal trauma and spinal anesthesia. In our case, it is presumed that repeated spinal operations or myelographies played a role as a trigger toward ossification.